The invention provides a blast device which is arranged in a grate. The blast device comprises a first blast pipeline and a gas distribution device, wherein the first blast pipeline is communicated with a hot blast source, the gas distribution device is arranged under a grate bed of the grate and is communicated with the first blast pipeline, and the gas distribution device comprises a plurality of ventilation parts with upward ventilation directions. Compared with the prior art, hot blast which comes from the hot blast source can be sufficiently mixed with low-temperature gas which passes through a material layer under the grate bed, the temperature of mixed gas can be increased above an acid dew point of the mixed gas by controlling the blast volume of the hot blast source to prevent dew, and therefore, the corrosion of the grate bed of the grate, a supporting roller for supporting the grate, a blast box and other parts can be avoided. The invention also relates to the grate and a pellet preparation device.